Low-temperature hydrodechlorination of chlorobenzenes on platinum-supported alumina catalysts

Hydrodechlorination of chlorobenzenes on platinum (Pt)-supported γ-alumina and alumina Lewis superacid (AmLSA) catalysts was carried out at room temperature and ambient pressure using a fixed bed flow reactor and a semi-batch reactor. Both the catalysts indicated good activity for the hydrodechlorination, but the former was superior to the latter. The hydrodechlorinations of reactants C₆H_6−xCl_x (x=1, 2, 3) proceeded step-wisely to benzene and then cyclohexane via C₆H_6−yCl_y (y=x−1). The reactions seem to be promoted by the contribution of spillover hydrogen formed on the Pt-supported catalysts. The catalysts deactivated with reaction time and the amount of chlorine that accumulated on the Pt-supported γ-alumina catalyst in the hydrodechlorination of 1,4-dichlorobenzene for 3 h was near to that estimated from the converted reactant molecules. When the deactivated catalysts were treated in a stream of hydrogen above 503 K, the original activity was completely restored, but the deactivation phenomenon with reaction time was observed again.     

An FT-IR study of the conversion of 2-chloropropane, o-dichlorobenzene and dibenzofuran on V2O5-MoO3-TiO2 SCR-DeNOx catalysts

Spectra of the adsorbed species arising from contact of a V₂O₅-MoO₃-TiO₂ model SCR catalyst with ortho-dichlorobenzene (o-DCB) and dibenzofuran (DBF) and their evolution with the temperature are presented and discussed. Dichlorobenzene adsorbs weakly probably on Lewis acid sites through the chlorine atom. A very fast nucleophilic substitution on dichlorobenzene to a chlorophenate species occurs already at RT. On the contrary, adsorption of dibenzofuran is molecular, probably through the oxygen atom on Lewis sites. The aromatic rings of both molecules tend to be later oxidized to give carboxylate species. Parallel experiments with chloropropane show that dehydrochlorination occurs readily, hydrochloric acid is adsorbed quite weakly and that propene can be further oxidized. However, heavier oxidized species like cyclic anhydrides are also formed from chloropropane. The data suggest that the dechloration step of the phenyl ring could be not critical. On the contrary, the building-up of aromatic compounds from smaller molecules is possible and the oxidation of phenyl ring can be slow near reaction conditions. The possibility that the reaction between phenate species and chlorobenzenes give the “de novo” synthesis of dioxins is envisaged.     

二氯苯的生产技术进展

介绍了二氯苯的性质、生产方法及国内生产概况,概述了二氯苯的合成及分离技术进展,指出高效定向催化技术及溶剂萃取精馏-结晶技术是今后二氯苯生产技术的发展方向。     

Catalytic oxidation of 1,2-dichlorobenzene over ABO3-type perovskites

Several ABO₃-type perovskite oxides (A = La, Y, Nd or Gd; B = Fe, Mn, Cr or Co) have been investigated as catalysts for the oxidation of 1,2-dichlorobenzene (o-DCB), a model compound for the highly toxic polychlorinated dibenzodioxins. Initial transient and steady state activity measurements were conducted with all catalysts in the absence and presence of water. Perovskites containing Cr in the B-site were more active than perovskites containing other transition metals, with YCrO₃ being the most active catalyst among the different systems studied. Furthermore, YCrO₃ did not show any loss of its initial activity after several hours on stream. Other perovskites lost 10–20% of their initial activity within the first 5–10 h on stream. This loss was associated with a corresponding loss in BET surface area. With the exception of LaCoO₃, all perovskites retained their crystalline structure upon exposure to o-DCB under reaction conditions. LaCoO₃ was converted to LaOCl and Co₃O₄. The presence of water appeared to enhance the catalytic activity of some perovskites. This effect can be attributed to a faster removal of Cl⁻ ions from the catalyst surface via their reaction with water.     

The catalytic hydrodechlorination of mono-, di- and trichlorobenzenes over supported nickel

The gas phase hydrodechlorination (HDC) of chlorobenzene (CB), chlorotoluene(s) (CT), 3-chlorophenol (3-CP), dichlorobenzene(s) (DCB) and trichlorobenzene(s) (TCB) over the temperature range 473 K≤T≤573 K has been studied using 1.5% and 6.1% (w/w) Ni/SiO₂ catalysts; the catalytic data have been obtained in the absence of any appreciable short-term deactivation. HDC of DCB and TCB generated the partially or the fully dechlorinated aromatic product + HCl and there was no significant cyclohexene or cyclohexane in the effluent stream. The conversion of mono-chloroarenes yielded the following reactivity sequence CB < 2-CT < 3-CT < 4-CT < 3-CP, i.e. the presence of an electron donating ring substituent enhances HDC and steric hindrance lowers reactivity. HDC kinetics have been adequately represented by a pseudo-first order approximation. Chlorine removal from DCB and TCB isomers proceeded through sequential and concerted routes, the relative importance of each dependent on the nature of the isomer and reaction conditions; apparent HDC activation energy increases in the order CB < DCB < TCB. The relationship between dechlorination selectivity and residence time/fractional conversion is addressed. The higher Ni loaded catalyst delivered consistently higher (specific) dechlorination rates and higher benzene yields from a polychlorinated feedstock. Catalytic HDC over Ni/SiO₂ is presented as a viable means of treating/detoxifying concentrated chlorinated gas streams and the best strategy for generating the parent benzene or a target partially dechlorinated product is discussed.     

电子束辐照降解二氯苯废水的研究

二氯苯是重要的有机污染物,采用常规处理方法难以降解.利用束流为1 mA、电子束能量为1.5 MeV的高能电子束辐照处理邻,间,对-二氯苯的模拟废水.辐照剂量分别为35 kGy、70 kGy、105 kGy、140 kGy、210 kGy.实验表明电子束能够降解氯苯类废水且效果很好,邻二氯苯、间二氯苯、对二氯苯的降解率为50%时所需剂量分别为:38 kGy、35 kGy、46 kGy.辐照降解过程中氯离子的质量浓度增加,辐照后溶液呈强酸性,pH在2-3.根据实验结果,本文给出了二氯苯的辐照降解机理并初步探讨了辐解中间产物的类型.     

吹扫捕集毛细管气相色谱法测定水中挥发性芳香烃化合物

介绍了吹扫捕集毛细管气相色谱测定水中挥发性含苯环有机物的方法。采用吹扫捕集装置对水中的目标分析物进行富集,选用VARIAN的毛细管色谱柱进行分离,氢火焰离子化检测器进行测定,线性相关系数均大于0.99,RSD小于10%,加标回收率在85%～100%之间,最低检出限满足国家标准的检验要求。